In the pre 2015 refugee crisis Europe there were a mix of everything from progressive social democratic parties to the dictatorship of Belarus and moderate and conservative liberal in the mix
The European far right have not become mainstream, some of it have but lot of it are still persona non grata in polite company.
But if you want a date for when it became possible for these party to go mainstream in the EU, it would be in 1999 with Austrian election, where FPÖ joined the coalition government and the embarassing reaction from the 14 other EU toward this, showed that a cordon sanitaire against democratic far right parties was no long possible.
